The problem:
Orders have the status Failed in Shiptheory and are providing the error seen in the image below. 
The Solution:
The first thing you should try is to Retry the order. This can be done from the Dashboard by clicking the blue arrow to the right of it and retry option.
If the order still has this error message, it is most likely an issue with the order itself within WooCommerce.
Check the product within the order has a Product ID assigned to it within WooCommerce. When viewing the product within the order, it should look like the image below where the name of the product redirects to the product's page within WooCommerce.
If it does not look like the above image, this may be where the issue is stemming from as Shiptheory is unable to location the order due to it not containing any product IDs. You may want to consult with your WooCommerce developer to resolve this.
Once a product ID has been added, you can once again click the Retry button on the order to bring it through into Shiptheory again, with the new product information.
Have any questions about this? One of our Support Team would be happy to give you a hand.